1 -c;,, State Hort. Soc. :-. 2000. proc. rw- COMPARISON OF YIELDS BY TREE AGE AND ROOTSTOCK IN SOUTHWEST FLORIDA ORANGE GROVES M. ROKA AND ROBERT E. ROUSE University of Florida,!FAS Southwest Florida Research and Education Center 2 State Road 2 North lmmokalee, FL 1 2 FRITZ Red ' varieties through thirteen years of age. Further, yield differences between and rootstocks are discussed. This paper updates earlier results reported during the 1 FSHS conference in Orlando (Roka, et al., 1). Materials and Methods P. MURARO University offlorida,!fas Citrus Research and Education Center 00 Experiment Station Road Lake Alfred, FL 0 RONALD,1dditional index words. Citrus sineis,,, Swinctle, pounds solids, high deity plantings. t ;,{bstract. A study to provide citrus managers with information on high deity citrus plantings in southwest Florida was ini" uated in the early s. The first report has been published (Roka et al., 1), providing yield data for '' and '' sweet oranges [Citrus sineis (L.) Osb.] for nine-year-old trees. This paper is a summary of the southwest Florida yield study for trees 1 years of age. Analysis of yield compariso between citrumelo (C. paridisi x Poncirus trifoliata) and citrange (C. sineis x P. trifoliata) rootstocks found a numerical but not coistent statistical difference under commercial production. Citrus acreage in southwest Florida expanded from 2,0 acres in 1 to 1,0 acres in 1 (Fla. Ag. Stat. Serv. (FASS), 1-). Much of this southern expaion was ':a result of growers' decisio to achieve a measure of freeze p rotection. During the s devastating freezes destroyed Jnore than 220,000 acres of Florida citrus, primarily in the,northern production region (i.e., Lake, Orange, Marion, and Pasco Counties) (Attaway, 1). For many growers, it was their first experience growing citrus under southwest Florida climate and soil conditio. In addition to new growing conditio, tree deities in the new plantings increased from the previous state average of 0 trees per acre in 1 to more than trees per acre in 1 (FASS, Commercial Citrus Inventory, 1, 1). Southwest Florida growers had little published information to guide them in setting realistic yield expectatio. Much of their information was based on yield-age profiles developed by Zach Savage during the s. Savage's yield profiles, however, reflected deep-sand, central ridge growing conditio and tree deities between and 0 trees per acre (Savage, ). In, members of the Southwest Florida Citrus Advisory Committee requested that new yield profiles be developed for the important citrus varieties being grown in the southwest Florida flatwood region. The objective of this paper is to summarize the yield data collected from southwest Florida groves and present yield profiles for '', '', and 'Rohde Florida Agricultural Experiment Station Journal Series No. N-01. Proc. Fla. State Hort. Soc. : 2000. The current study was initiated in 1 by soliciting grower-cooperators to provide annual yield data from selected blocks. The study blocks had to have been planted since 1, planted to a single scion-rootstock combination, and managed uniformly. Blocks were chosen to represent "typical" growing conditio within the grove. Neither the best nor poorest blocks were to be included in the study. Block size (net tree acres) was not controlled. By assuming that a block (whatever size) was managed as a single unit, yield data from individual blocks could be reduced to boxes and pounds solids per acre. Further, by not controlling block size, the study did not impose additional record keeping burde on grove personnel. After a block was selected, the grove manager filled out a general information sheet, describing block size, planting date, tree spacing, bed configuration, irrigation system, predominate soil types, and general fertilization practices. Annual harvest data were requested from the time the block had been planted. Harvest data included total boxes harvested for the fresh market, boxes harvested for processing, and total pounds solids delivered to the processing plant. Grove managers were also asked to report the number of trees removed and reset annually, whether the block had been hedged or topped, and approximate fertilization rates. Data summary sheets were developed for each block. At the end of each subsequent harvest period, the summary sheets were sent back to the grove managers for updating. Tree age in this study was referenced agait a 1 May planting date. For any block planted prior to 1 May in a given year, the harvest season of that calendar year was counted as "year one." For blocks planted after 1 May, "year one" did not begin until the next calendar year. For example, year-one for a block planted Apr 1 was the 1- harvest season. Alternatively, year-one for a block planted June 1 was the 1- harvest period. A 1 May date was selected as a reference planting date because it eured that all blocks of the same age cohort would have gone through the same number of possible bloom cycles. Data from the summary sheets were organized into spreadsheets and sorted by scion variety, rootstock, and tree age. Despite being planted in different years, yields of similar aged blocks were grouped and analyzed together. Annual harvest data from the blocks were converted to boxes per acre and pounds solids per box. In this paper, pounds solids per acre were derived by multiplying average boxes per acre by average pounds solids per box. For each sorted group, mea and standard deviatio were calculated by tree age for boxes per acre and pounds solids per box. Statistical differences in yields among scion varieties and rootstocks were analyzed using the standard T-test.
Initial study blocks included only four scion variety-root-. stock combinatio-'' /, '' /, ''/, and ''/. Over the next few years, the range of study blocks expanded to include 'Rohde Red ' and red grapefruit scion varieties. By 1, the study was tracking blocks, representing nearly,000 acres. blocks were added to the study in 1 to increase diversity with respect to tree deity and rootstock selection. The results presented in this paper represent almost,00 acres of round orange production from individual blocks. Data from an additional 0 acres of grapefruit production were also collected, but this paper discusses only the data collected from round orange production. Table 1 lists the acreage and number of blocks by variety and rootstock. With the completion of the 1/ -harvest season, fourteen blocks had reached 1 years of age. A few blocks are being tracked that were planted more than 1 years ago. However, a criteria of the study is not to report an annual yield value if there are less than four blocks with data at a given tree age. Table 2 summarizes the study blocks by scion variety, block size, tree age, and tree deity. Blocks ranged from nine to 2 net tree acres. On average, blocks are between and net tree acres. All study blocks are at least six years old and the average tree age for all scion varieties is between and years. A few blocks are as old as 1 years. Tree deity averages near trees per acre. Tree deity ranges from a '' block of1 trees per acre to a 'Rohde Red ' block with 2 trees per acre. Coincidentally, the 'Rohde' block with 2 trees per acre is also the youngest block in the study (six years old). All blocks were planted on two row beds and were irrigated. Except for ten blocks, which utilized seep irrigation, low volume micro-jet irrigation systems were in place on the study blocks. For the most part, the study cooperators are part of large, well-organized citrus operatio. These operatio perform good grove management practices and keep accurate records of their harvests and production inputs. Therefore, it is expected that the averages reported in this paper would be above state-wide production averages. Results and Discussion Variety differences. Average boxes per acre increased through nine years of tree age for each scion variety, regardless of rootstock. Table presents average boxes per acre by Table I. Number of study blocks, acreage, and participating groves b s, and rootstock. Y C i r~;: Block N~ Variety / Rootstock (no.) A_c_r_e_ag:_e of-:::.groves Rohde Red Total Orange Blocks Grapefruit Total Study 2 1 1 22 1 1 1 2,,, 0,2 ------ ' roots tocks include, rough lemon ( C. jambhin), cleo ( C. reshnz), and sour orange ( C. aurantium). tree age for '', '', and 'Rohde Red ', Table presents average pounds solids per acre by tree age for the same three scion varieties. Since tree age cohorts were planted in different years, the values in Tables and should be interpreted as long-run expected averages by tree age. By grouping similar aged blocks planted in different years, seasonal weather and production variability have been averaged; '' blocks peaked at 2 boxes per acre in year ten. By age nine, '' blocks produced an average of nearly 00 boxes per acre, while 'Rohde Red ' approached 0 boxes per acre. Between nine and twelve years, production plateaued with '' blocks producing between 02 and 2 boxes per acre and '' blocks producing between 2 and 1 boxes per acre. Average production in 1 year old trees dropped to boxes per acre, more than a ten percent decline from the previous year. However, it was unclear wheth er this reduction is a reflection of a limited number of 1 '.) year old blocks ( blocks), or whether trees systematically start to Ii Table 2. Summary statistics describing net tree acres, tree age, and tree deity of the study blocks. Scion (number of blocks) Units Avg Minimum Maximum (2) ( ) Rohde ( 1) Acres 1 Tree age (yrs) 1 Deity (trees/ acre) 1 1 1 Acres 1 Tree age (yrs) 1 Deity (trees/ acre) 1 1 Acres 1 2 Tree age (yrs) 1 Deity (trees/ acre) 1 2 Proc. Fla. State Hort. Soc. : 2 ( loo
fabl e. Average boxes per acre by tree age for '', '', and 'Rohde Red ' and indication of statistical significant yield differences ' berween '' and '' and between '' and 'Rohde Red ' as measured by T-tests.' free Age g 1 1 2 02 2 0 1 Boxes per acre 1 202 0 1 1 2 1 An'*' indicates the difference between the two mea is significant at the % confidence level. An '' indicates no significant difference between the two mea. Rohde vs. vs. Rohde 1 0 1 2 0 2 2 decline. Thirteen year old '' and 'Rohde Red j blocks appeared to be maintaining their production levels. Again, however, both scion varieties have a limited number of blocks at that age, five and two blocks, respectively. From three years of tree age onward, '' blocks produced more boxes per acre than did '' blocks. These yield differences became statistically significant by six years of tree age when '' blocks produced between 0 and 0 more boxes than '' blocks. Statistically significant yield differences between standard '' and 'Rohde Red ' blocks were not found among the respective study blocks. An important caveat to note is that scion clone identification numbers were not collected with the study block data. Data from the Southwest Florida Budwood Foundation Grove have indicated wide production variability among Rohde clones (Rouse and Youtsey, 1; Rouse, 2000). Pounds solids per box increased through the first ten years of tree age for all scion varieties (Table ). Pounds solids per box appeared to reach a plateau between ten and thirteen years of tree age. At every tree age, more pounds solids per box are produced from '' than from '' trees. The differences were statistically significant after four years. Eight year old 'Hamli' produced.2 pounds solids per box. Eight year old 's' produced.1 pounds solids per box, 1. pounds solids per box more than 'Hamli'. Pounds solids per box were not significantly different between standard and 'Rohde Red ' clonal selectio through 1 years of tree age. Multiplying average boxes per acre with average pounds solids per box provided an estimate of pounds solids per acre by tree age. While a statistical test was not possible, it appears that after age five, '' blocks coistently yield more pounds solids per acre than do '' blocks (Table ). Average '' blocks peaked at more than,000 pounds solids during year ten, while maximum pounds solids production on a '' was 2,0 during year nine. Between seven and thirteen years of age, 'Rohde Red ' blocks produced between 2,200 and 2,00 pounds solids per acre, annually. There does not seem to be any clear year-to-year pattern when pounds solids production from Rohde blocks were compared agait standard '' blocks. &otstock differences. The study blocks were further sorted and analyzed to determine whether and had an effect on production. A stated hypothesis among growers and researchers is that, a more vigorous rootstock, would produce greater yields. To some extent, yield averages Table. Average pounds solids per box by tree age for '', '', and 'Rohde Red ' and indication of significant yield differences between '' and '' and between '' and 'Rohde Red ' as measured by T-tests.Z Tree Age Rohde vs. vs. Rohde Pounds solids per box 2..0 na..0..1.1.0.0....1...0.2.2.1.2..2..1..1...... 1.0..2 'An "*" indicates the difference between the two mea is significant at the % confidence level.. An '" indicates no significant difference between the two mea. * * Proc. Fla. State Hort. Soc. : 2000.
Table. Estimated average pounds solids per acre by tree age for '', '', and 'Rohde Red ' variety in southwest Florida.' Tree Age Rohde Pounds solids per acre 1,2 l, 1,0 1,0 2,0 2,0 2, 1,2 2, 2,1 2,22 2,2 2,21 2, 2, 2,0 2,1,0 2,2 2, 2, 2,02 2,1 2, 2,2 2, 1 2,0 2,20 2,21 'Table values derived by multiplying corresponding values from Tables and (box/acre* ps/box). presented in Table confirm this belief. In nine out of ten years, the average yields from '' blocks with rootstocks were numerically greater than blocks with rootstocks. On '' varieties, blocks outperformed blocks six out of ten years. Figures 1 and 2 illustrate the numerical differences in mean production between and rootstocks over the age profile. When statistical tests were applied, however, data from the study blocks failed to show any statistically significant yield differences between and rootstocks both in terms of year-to-year compariso and in terms of cumulative yield compariso (Table ). This "statistical iignificance" contradicts the common perception by suggesting that. observed yield differences between the two rootstocks are more to chance than real horticultural effects. Perhaps and grove management practices, which this study cannotfi ly isolate, are masking production effects from these two rob ~ stocks. Alternatively, the r?ots~ock ~ffect may be real, but i~~ overall effect on commercial yields is small. ~l vytiile the study blocks may not indi~ate a. sign~cant p$e ' ductn effect from rootstocks, tralatmg yield d1fferenc~ :, into economic terms suggest that growers do, in fact, see aw' economic gain from planting trees with rootstocks. ' an exercise, it was assumed that paired blocks of '' a '' were planted to and rootstock 1 1 and began to bear fruit during their third year, 1 The yield differences, shown in Table, were valued using early I mid and late season average on-tree prices reported the Florida Agricultural Statistics Service (FASS, 1-)~" The right-hand colum of Table show the annual mon~: ~ tary value of having planted rootstock. Over the te ';,c-;' year period, from 1-1, annual per-acre gross revenu from a '' block planted on would have be~, $22 higher than a '' block planted on. The.:i differences were not as dramatic with '' varieties, b,~~w revenues from blocks were on average $ per ac higher than revenues from blocks. Conclusio The Southwest Florida Citrus Yield Study is an ongoing:. project to develop yield-age profiles for selected citrus scion ' varieties and rootstocks in southwest Florida. This paper pr~);~ ''i:,.,_, Table. Monetary valuation of yield differences between and roots tocks for '' and '' sweet orange trees. =============================================================~~r Production Season avg Annual Cum. Difference price valuey value Age $/bx $/acre $/acre -1~ r.,_~,, 2 21 1 ( - ) 2 21 2 1 0 0 0 0 -..01...2..2.2.1 2.1 Annual Avg $/acre $1 $ $20 $ $21 $1 $2 $1 -$02 $ $22 $1 $ $1,1 $1, $1,1 $2,0 $2,2 $2, $2, $2,2 21 2 0 0 1 1-1 1 1 22-0 1 20 - -1 0 2 22.1.....1.1..0. Annual Avg $/acre -$ $2 $ $2 -$ $ -$1 -$0 $ $ $ -$ $ $ $2 $ $2 $20 $ $22 $ 'Season average on-tree prices for early/mid and late season varieties as reported by Fla. Agricultural Statistic Service from 1/ through 1/ season. YAnnual value equals the season average on-tree price multiplied by the yield differences between and blocks. Proc. Fla. State Hort. Soc. : 2000.
0 00 00 00 ~ (.J a; fl,.,:i) ~ 0 Ill <( 00 - - 00-0 Q; 00 a. 20 -- I/) - Q) x 0 co 200-200 0 0 1 Years in Age 1 Yearsjn Age Figure 1. Estimated boxes per acre for '' by tree age and sorted by,\ingle and rootstocks. Figure 2. Estimated boxes per acre for '' by tree age and sorted by and rootstocks. sents average yields for '', '', and 'Rohde Red ' scion varieties through 1 years of tree age. '' blocks generally outperform '' blocks in terms of Literature Cited boxes and pounds solids per acre. The reverse is true in terms of pounds solids per box, where '' scion varieties pro' duce more than '' scion varieties. While these results may confirm what growers already knew, this study provides growers with a benchmark from which to evaluate the perfor~ mance of their own groves. Given the above average level of management among the growers who are participating in this study, the average yields reported from this study are likely to be higher than a region-wide average. However, long-term success will require a grower to set production goals at a level higher than a region-wide average. Therefore, the benchmark provided by this study should help growers achieve long-term success. Attaway, J. A. 1. A history of Florida citrus freezes. Fla. Science Source, Inc. Lake Alfred, FL. Florida Agricultural Statistical Service, Annual citrus summaries, 1-1. Fla. Agr. Stat. Serv., Orlando, FL. Florida Agricultural Statistical Service, Commercial citrus inventories,. Fla. Agr. Stat. Serv., Orlando, FL.. Roka, F. M., R. E. Rouse and R. P. Muraro. 1. Southwest Florida citrus yield by tree age in high deity plantings. Proc. Fla. State Hort. Soc. 0:2-. Rouse, R. E. and C. 0. Youtsey. 1.Juice quality from young trees of clones on 1 rootstocks in the Immokalee Foundation Grove. Proc. Fla. State Hoit. Soc. :-. Rouse, R. E. 2000. Citrus fruit quality and yield of six clones on 1 rootstocks in the Immokalee Foundation Grove. Proc. Fla. State Hort. Soc. :(1n press). Savage, Z.. Citrus yields per tree by age. Economic Series 0-, Food and Resource Econ. Dept., Univ. of Fla., Gainesville, FL. Proc. Fla. State Hart. Soc. :-. 2000. EVALUATION OF ORANGE TREES BUDDED ON SEVERAL ROOTSTOCK$ AND PLANTED AT HIGH DENSITY ON FLATWOODS SOIL MONGI ZEKRI University offlorida, IFAS Hendry County Exteion Office Pratt Boulevard. LaBeUe, FL Additional index words. Citrus, financial analysis, fruit quality, fruit yield, growth, juice color, mineral concentration. Abstract. The performance of '' orange trees on citrumelo (Swi), Cleopatra mandarin (Cleo), Milam lemon {Mil), and Volkamer lemon (Volk) rootstocks was evaluated on the flatwoods soil of southwest Florida. Leaf mineral concentration, growth, fruit production and quality were measured four and seven years after planting in a closely-spaced setting (1 ft by ft) in a commercial grove. Compared to Florida citrus Florida Agricultural Experiment Station Journal Series No. N-0. Proc. Fla. State Hort. Soc. : 2000. leaf standards, leaf mineral concentration values were within the optimum to the high range. Yield efficiency expressed as lb solids/yard of canopy and juice quality in terms of juice content, Brix, and lb solids/box increased with tree age. Tree and fruit size were the highest for Volk and the lowest for Cleo. Fruit yield was the highest for Volk. However, yield expressed in lb solids/acre was not significantly different between Volk and Swi due to the higher solids/box for Swi. Yield efficiency was also higher for Swi than for Volk. Juice content and soluble solids in the fruit were higher for Swi and Cleo than for both lemon rootstocks. Financial analysis showed that at high deity planting, trees on Swi were the most profitable. Citrus is of major economic importance in many counties of Florida, with a total economic impact exceeding $ billion a year. In Florida, citrus groves occupy approximately,000 acres with over million trees (Florida Agricultural Statistics Service, 1). Rootstocks have had a substantial role in the development of the Florida citrus industry. Prior to about